A tunnel diode represented by an Esaki diode is known as a conventional negative-resistance device (for instance, in Patent Document 1). The negative resistance shown by the tunnel diode originates in a tunnel phenomenon, and in the case of the Esaki diode, for instance, the negative resistance is realized by enhancing impurity concentrations of P type and N type in a PN junction diode.
FIG. 1 illustrates current/voltage characteristics of an Esaki diode which has been prepared from various materials (Ge, GaSb, Si and GaAs). FIG. 2 schematically illustrates these characteristics. Reference numeral 21 in FIG. 2 denotes a negative-resistance region which exists in current/voltage characteristics. Such a device as exhibiting a negative resistance which is specific electrical conduction characteristics can be applied to an oscillator, an amplifier, a mixer, a switching device, and the like.
It is also proposed to use a magneto-resistive effect device as a magnetic memory device, which has a ferromagnetic tunnel junction having a first ferromagnetic layer, an insulation layer and a second ferromagnetic layer stacked therein (for instance, in Patent Document 2). The magneto-resistive effect device also has current/voltage characteristics including a negative-resistance region.
Patent Document 1: Japanese Patent Publication No. S35-006326
Patent Document 2: Japanese Patent Application Laid-Open No. 2004-158750
Current/voltage characteristics of an Esaki diode is expressed by the sum of electric current components having three different components of a tunnel current, an excessive current and a diffusion current. Therefore, the current/voltage characteristics show not only an excellent linear region but also a non-linear region over a wide range as is illustrated in a region 22 in FIG. 1. Such existence of a non-linear region causes a problem that when the diode is applied to an amplifying apparatus, the amplifying apparatus cannot obtain a stable gain.
In addition, in the Esaki diode, a voltage region showing negative resistance is determined by a band gap of a material. Accordingly, the voltage region developing the negative resistance is determined by the material, so that a negative-resistance device having a different voltage region cannot be prepared by the same materials.
A magneto-resistive effect device having a ferromagnetic tunnel junction disclosed in Patent Document 2 also shows the negative resistance, but the current/voltage characteristics include a large non-linear region similar to the Esaki diode.